I mean, during HG/SS, the dive application was more interactive, but the movement underwater was less than satisfactory. There wasn't any thick seaweed to travel through to find Pokemon, it was more like a cave.

HGSS didn't have dive in it. Did you mean BW/B2W2?

I'm also not sure what a sequel to RSE where the canon of those games is retconned by things being destroyed would actually achieve in terms of gameplay. Nor is a Hoenn reboot a given to happen in the first place, for that matter.